1. Field of the Invention
The present invention relates to a probe with torsion lever structure and a scanning probe microscope and a record/reproducing apparatus utilizing the probe.
2. Related Background Art
The recently developed scanning tunnel microscope (STM) [G. Binning et al., Phys. Rev. Lett., 49, 57(1982)] is capable of directly observing the electron structure of surfacial atoms of a conductive material, whereby both monocrystalline materials and amorphous materials can be observed by a real spatial image of a resolving power.
Such STM, capable of observation with a low electric power without damage by current on the specimen and of functioning on various materials even in the atmospheric condition, is expected to be used in wide applications.
The STM utilizes a tunneling current generated between a metal tip and a conductive substance when they are brought close to a distance of about 1 nm, with a voltage therebetween. This current is extremely sensitive to the variation in the distance between the two, and various information on the electron cloud in the real space can be detected by moving the tip in a scanning motion so as to maintain the tunneling current constant. In this operation there can be obtained a resolving power in the order of 0.1 nm along the plane of the specimen, so that high-density information recording and reproduction in the atomic (sub nanometric) order can be sufficiently realizable by the principle of the STM.
For example, there have been proposed a methods of effecting information recording and reproduction by the STM, utilizing a thin film of an organic compound with .pi.-electrons or a chalcogenide compound, which shows memory effect for the switching characteristics of voltage or current, as the recording layer, as disclosed in the Japanese Patent Laid-open Application Nos. 63-161552 and 63-161553.
These methods, with a bit size for example of 10 nm, enable large-capacity information recording of a high density as high as 10.sup.12 bit/cm.sup.2.
For compactizing the apparatus, there is being developed a micromechanical technology of forming plural probes with extremely small movable mechanisms on a semiconductor substrate, through a microphotolithographic process.
The typical micromachine employable in the movable mechanism of such probe can be, for example, an electrostatic cantilever or a piezoelectric bimorph cantilever, as proposed in the U.S. Pat. No. 4,906,840. Such micromachines can be produced by a microphotolithographic process, thus being easily formed as an array with a low cost, and can achieve high-speed response by the compactization. Particularly the electrostatic cantilever, effecting displacement by an electrostatic attracting force generated by an external voltage application, can achieve a larger displacement for a given size, in comparison with the piezoelectric bimorph cantilever which effects displacement spontaneously.
There has also been proposed a structure of electrostatically driving a flat plate portion, maintained on a beam member supported on both ends, utilizing the torsion elasticity thereof (such structure being hereinafter called torsion lever probe), as proposed in the Japanese Patent Laid-open Application No. 4-1948.
In contrast to the cantilever structure, such torsion lever probe can be formed as a microdisplacement device with increased freedom in the rigidity and the resonance frequency, since the bending elasticity of the lever and the torsion elasticity of the beam can be independently selected. Also in contrast to the electrostatic cantilever in which the distance to the opposed specimen is difficult to control as the end of the lever moves toward the specimen under the voltage application, the torsion lever structure has an advantage of easier control of the distance to the specimen as the lever end moves in a direction opposite to the specimen under the voltage application.
FIG. 1 is a perspective view of a torsion lever probe, and FIGS. 2A and 2B are cross-sectional views thereof along a line 2--2 in FIG. 1, respectively in a non-driven state and a driven state of the probe.
Referring to FIG. 1, a substrate 501 is provided thereon with an insulating layer 502, on which formed are a fixed electrode 503 and a flat plate driving unit 508 across a gap 504.
The flat plate driving unit 508 is rotatably supported, through two beams 509 supported at both ends thereof, by support portions 510. The flat plate driving unit 508 is divided into two areas by the rotary axis passing through the beams 509, and an upper driving electrode 507 is formed in one of said areas, opposed to the fixed electrode 503, while a tip 512 for information input/output, connected electrically to a tip wiring 513, is formed at the end of the other area.
In the above-explained structure, an electrostatic attractive force is generated between the fixed electrode 503 and the upper electrode 507 by the application of a voltage therebetween, whereby the upper electrode 507 of the flat plate driving unit 508 is attracted toward the fixed electrode 503. Thus the beams 509 are twisted and the flat plate driving unit 508 rotates about the supporting beams 509 whereby the tip 512 is moved in a direction away from the substrate 501 (cf. FIG. 2B). Such movement can be utilized for controlling the distance between the tip 512, formed at the end of the flat plate driving unit 508, and the recording medium or observed specimen (not shown).
In such torsion lever probe, however, the movable distance of the tip is limited to the magnitude of the gap, namely the distance between the fixed electrode and the end of the flat plate driving unit, since said flat plate driving unit is rotated about the supporting beams. If the rotary axis of the beams is formed at the center of the flat plate driving unit, the movable distance of the tip cannot exceed the magnitude of the gap.
Though it is conceivable to increase the movable distance of the tip by increasing the magnitude of the gap and positioning the flat plate driving unit at a larger distance from the substrate, but such configuration will require a significantly increased electrostatic driving voltage, which may result in various drawbacks in the practice.